Generalize RETURNING and suppor for MariaDB / SQLite

As almost every dialect supports RETURNING now, RETURNING
is also made more of a default assumption.

* the default compiler generates a RETURNING clause now
  when specified; CompileError is no longer raised.
* The dialect-level implicit_returning parameter now has
  no effect.   It's not fully clear if there are real world
  cases relying on the dialect-level parameter, so we will see
  once 2.0 is released.   ORM-level RETURNING can be disabled
  at the table level, and perhaps "implicit returning" should
  become an ORM-level option at some point as that's where
  it applies.
* Altered ORM update() / delete() to respect table-level
  implicit returning for fetch.
* Since MariaDB doesnt support UPDATE returning, "full_returning"
  is now split into insert_returning, update_returning, delete_returning
* Crazy new thing.  Dialects that have *both* cursor.lastrowid
  *and* returning.   so now we can pick between them for SQLite
  and mariadb.  so, we are trying to keep it on .lastrowid for
  simple inserts with an autoincrement column, this helps with
  some edge case test scenarios and i bet .lastrowid is faster
  anyway.  any return_defaults() / multiparams etc then we
  use returning
* SQLite decided they dont want to return rows that match in
  ON CONFLICT.  this is flat out wrong, but for now we need to
  work with it.

Fixes: #6195
Fixes: #7011
Closes: #7047
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7047
Pull-request-sha: d25d5ea3abe094f282c53c7dd87f5f53a9e85248

Co-authored-by: Mike Bayer <mike_mp@zzzcomputing.com>
Change-Id: I9908ce0ff7bdc50bd5b27722081767c31c19a950

1 files changed, 10 insertions, 33 deletions

diff --git a/lib/sqlalchemy/dialects/oracle/base.py b/lib/sqlalchemy/dialects/oracle/base.py
index 37b81e1dd..faac0deb7 100644
--- a/lib/sqlalchemy/dialects/oracle/base.py
+++ b/lib/sqlalchemy/dialects/oracle/base.py
@@ -293,40 +293,16 @@ added in a future release.
 RETURNING Support
 -----------------
 
-The Oracle database supports a limited form of RETURNING, in order to retrieve
-result sets of matched rows from INSERT, UPDATE and DELETE statements.
-Oracle's RETURNING..INTO syntax only supports one row being returned, as it
-relies upon OUT parameters in order to function.  In addition, supported
-DBAPIs have further limitations (see :ref:`cx_oracle_returning`).
+The Oracle database supports RETURNING fully for INSERT, UPDATE and DELETE
+statements that are invoked with a single collection of bound parameters
+(that is, a ``cursor.execute()`` style statement; SQLAlchemy does not generally
+support RETURNING with :term:`executemany` statements).  Multiple rows may be
+returned as well.
 
-SQLAlchemy's "implicit returning" feature, which employs RETURNING within an
-INSERT and sometimes an UPDATE statement in order to fetch newly generated
-primary key values and other SQL defaults and expressions, is normally enabled
-on the Oracle backend.  By default, "implicit returning" typically only
-fetches the value of a single ``nextval(some_seq)`` expression embedded into
-an INSERT in order to increment a sequence within an INSERT statement and get
-the value back at the same time. To disable this feature across the board,
-specify ``implicit_returning=False`` to :func:`_sa.create_engine`::
+.. versionchanged:: 2.0  the Oracle backend has full support for RETURNING
+   on parity with other backends.
 
-    engine = create_engine("oracle+cx_oracle://scott:tiger@dsn",
-                           implicit_returning=False)
 
-Implicit returning can also be disabled on a table-by-table basis as a table
-option::
-
-    # Core Table
-    my_table = Table("my_table", metadata, ..., implicit_returning=False)
-
-
-    # declarative
-    class MyClass(Base):
-        __tablename__ = 'my_table'
-        __table_args__ = {"implicit_returning": False}
-
-.. seealso::
-
-    :ref:`cx_oracle_returning` - additional cx_oracle-specific restrictions on
-    implicit returning.
 
 ON UPDATE CASCADE
 -----------------
@@ -1572,8 +1548,9 @@ class OracleDialect(default.DefaultDialect):
     supports_alter = True
     max_identifier_length = 128
 
-    implicit_returning = True
-    full_returning = True
+    insert_returning = True
+    update_returning = True
+    delete_returning = True
 
     div_is_floordiv = False